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ACU-M™ Improving In-Building Communications

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ACU-M™ Improving In-Building Communications Application Note: AN-2306-2 ACU-M™ Improving In-Building Communications Purpose This application note will describe methods in which the Raytheon’s ACU-M can be used to improve in-building communications. The application note will discuss permanent and temporary methods at which different devices can help increase the ability to transmit or receive land mobile radio communications from within a building, below-grade, or behind obstructions. Introduction Land mobile radios, whether used in vehicles or as handheld portables, are an important tool used everyday by first responders to make their jobs safer and more efficient. In the most part, these radio systems function as designed, and serve the end-user with reliable communications. However, when the duties of a first responder require them to enter a building, or operate below- grade during emergencies, the ability of their radios to communicate to the base, incident command or dispatcher may become an issue. One physical constraint of land mobile radio communications is its inability to transmit and receive radio waves through obstructions such as buildings or below-grade structures. The failure of a land mobile radio to transmit and receive communications from within a building or below-grade has cursed radio users since the beginning of land mobile radio communications (see Figure 1). Figure 1: Blockage or Absorption of Low-Power Handheld Radio Transmission Raytheon 5800 Departure Drive Raleigh, NC 27616 919.790.1011 © Raytheon Company. Data is subject to change. http://www.raytheon.com All Trademarks are the property of their respective owners. Application Note: AN-2306-2 Solutions Land mobile radios were first introduced to public safety, in the late 20’s, in the form of shortwave receivers mounted inside patrol vehicles. The earlier radio systems, used by the Detroit Police Department allowed only one-way transmissions from the headquarters to the patrol vehicle. It was never certain that the officer actually received the transmission. As technology progressed, communications allowed the officer to converse with the dispatcher in a two-way, half-duplex fashion. This occurred in the 30’s with the Bayonne Police Department. Officers were now able to communication to the dispatcher, headquarters and the other officers in the field. The natural progression was to make the mobile radio, portable, hence the handie-talkie or handheld land mobile radio. Officers and firefighters were now able to leave their vehicles and communicate with their dispatchers, commanders and amongst themselves with small radios that they can carry on their belts. One drawback of the handheld radio is its lack of transmit power (1 to 5 watts) to link to the main repeater of the radio system. Figure 2 shows that the mobile radio mounted inside a vehicle has a distinct advantage because it can usually transmit at much higher power levels (5 to 50 watts, or greater) than the portable radio, thus mobile mounted radios are more likely to link with the radio system’s repeater, even through obstructions, such as the building, below. Figure 2: High-Power Mobile is able to Penetrate Building Material Technologies such as receiver voters and comparators, multicast and simulcast are techniques used in today’s modern radio systems that help compensate for the performance of the lower powered handheld radios. These techniques leveled the playing field, making handheld radios just as important to the first responder, as their mobile radios inside their patrol cars or apparatus. However, when an officer or firefighter enters a structure he may be faced with the uncertainty that his handheld portable radio may not be able to reach the main repeater site or satellite receiver sites due to blockage as a result of the materials of the building surrounding him. Raytheon 5800 Departure Drive Raleigh, NC 27616 919.790.1011 © Raytheon Company. Data is subject to change. http://www.raytheon.com All Trademarks are the property of their respective owners. Application Note: AN-2306-2 Some agencies have migrated from lower frequency radios (VHF) to higher frequency radios (UHF, 800 MHz) to take advantage of the improved “penetrating” properties of the shorter wavelengths, in attempts to counteract the signal-attenuating properties of the building’s surface (see Figure 3). Although VHF transmissions can travel around very large obstructions and travel many more miles than 800 MHz transmissions, VHF is no match for dense urban locations, where reflection and absorption of VHF signals is prevalent. Figure 3: Improve Penetration, Shorter Wavelength is Better In the dense metro environment, more and more obstructions are blocking the desired line-of-site (LOS) between the handheld radio and the repeater, and even higher frequency radio systems are not the answer. Additionally, building materials such as concrete, foil-insulation, steel and Low-E-Glass (low-emission glass), which has a microscopically-thin coating of light blocking metal oxide, can completely isolate the radio user within a building. Permanent Solutions – Permanent in-building repeater systems can be used to create an electrical pathway that will allow transmissions to be routed from the inside of the building, to the outside of the building, through electronic means, and visa versa. One method is to place a receiver and donor antenna outside of the building to retransmit the low-power handheld radio transmissions that are picked up by distributed coverage antennas throughout the inside of the building. Figure 4 illustrates transceivers, roof-top donor antenna, distributed interior coverage antennas and cables used in a permanent in-building repeater system. The low-power transmissions from the officer’s portable radio can circumvent the RF absorbing or RF blocking properties of the building material, and utilize an electrical pathway to the donor antenna on top of the building. Conversely, transmissions can be received by the donor antenna on the rooftop, amplified, and then routed to the numerous coverage antennas within the building, which then allows the portable radio inside the building to receive transmissions from outside. There exists similar in- building communication systems that distribute transmit and receive communications over fiber optic lines. In all cases, the transceivers used in these systems are called Bi-Directional Amplifiers, BDA. Raytheon 5800 Departure Drive Raleigh, NC 27616 919.790.1011 © Raytheon Company. Data is subject to change. http://www.raytheon.com All Trademarks are the property of their respective owners. Application Note: AN-2306-2 Figure 4: Bi-Directional Amplifiers, Permanent Solution Instead of an array of transceivers, antennas and combiners, another method of signal distribution is to install a radiating cable or “leaky coax” along the vertical length of the building. The cable, with radiating slots along its length, would capture transmitted signals from the handhelds from within the building, and also leak transmitted signals receive from outside of the building, into the building from the donor receiver on the top of the building. Figure 5: Radiating Cable, Permanent Solution Figure 5 illustrates a permanent radiating cable solution that utilizes a BDA to facilitate the transceiver duties. Raytheon 5800 Departure Drive Raleigh, NC 27616 919.790.1011 © Raytheon Company. Data is subject to change. http://www.raytheon.com All Trademarks are the property of their respective owners. Application Note: AN-2306-2 Although municipalities have started requiring new and existing commercial and government buildings of certain sizes and construction types to be equipped with permanent in-building repeater systems, there are many more municipalities unable to fund or put forth such directives to change their local building codes. These ill equipped buildings have become potential death traps to first responders and the occupants that they are sworn to protect. Firegrounds Communications - Firefighters communicate using Hierarchal Communication system where the Incident Commander will communicate with several Team Leaders; and the Team Leader will communicate with the a 3 or 4 firefighter team inside the building. With this Social Communications Environment the Incident Commander will typically remain outside of the building relaying messages to the team leader inside of the building using land mobile radios. In some instances, the IC may enter the building using the floors below the incident as a command post. Whichever command structure is used at the firegrounds, this social method assures that no one person is responsible for too many tasks, the incident will remain modular, and since communications occurs in a hierarchal basis, this technique tends to reduce traffic and loading of the radio systems. Communications techniques used by firefighters are varied. Some rely on repeated systems, and some on a dispatch environment, where the IC communicates with the dispatcher, and the IC relays messages to the team leaders at the firegrounds. But once the firefighter teams enter a building or underground structure, many fire service agencies may have no choice, but to practice the use of simplex or tactical communications. Figure 6: Firefighters Often Use a Dispatch Communications Hierarchy In principle, simplex firegrounds communications is useful in an in-building incident because the radio communications using the main repeater between the incident commander, team leaders, and firefighters may not possible due to the RF blocking properties of the building’s surface. Figure 7 shows that the firefighters have switched their low-power handheld radios to a simplex firegrounds or tactical channel, and are now able to communicate in a localized fashion. The Incident Commander at the command post is also able to communicate with the personal inside Raytheon 5800 Departure Drive Raleigh, NC 27616 919.790.1011 © Raytheon Company. Data is subject to change. http://www.raytheon.com All Trademarks are the property of their respective owners. Application Note: AN-2306-2 the building by utilizing a radio in a similar simplex tactical mode. These radios operating in simplex mode must all transmit and receive using the same frequency.
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